59 a Preliminary Study of Small Scavenging

Malaysian Journal of Science 32 (2): 59-66 (2013)

A PRELIMINARY STUDY OF SMALL SCAVENGING CRUSTACEANS COLLECTED BY BAITED TRAPS IN A CORAL REEF OF BIDONG ISLAND, MALAYSIA

Ryota Nakajima1*, Teruaki Yoshida2, B. A. R. Azman2, Haruka Yamazaki3, Tatsuki Toda3, B. H. R. Othman2, Kassim Zaleha & A.W.M. Effendy4

1 Marine Biodiversity Research Program, Institute of Biogeosciences, Japan Agency for Marine-Earth Science and

Technology (JAMSTEC), Yokosuka, 237-0061 Kanagawa, Japan

2 Marine Ecosystem Research Centre, Faculty of Science and Technology, Universiti Kebangsaan Malaysia, 43600

Bangi, Selangor D. E., Malaysia 3 Department of Environmental Engineering for Symbiosis, Faculty of Engineering, Soka University, Hachioji,

192-8577 Tokyo, Japan

4 Institute of Tropical Aquaculture, Universiti Malaysia Terengganu, 21030 Kuala Terengganu, Terengganu, Malaysia 5 Institute of Marine Biotechnology, Universiti Malaysia Terengganu, 21030 Kuala Terengganu, Terengganu, Malaysia

* Corresponding address: 1 Marine Biodiversity Research Program, Institute of Biogeosciences, Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Yokosuka, 237-0061 Kanagawa, Japan

Abstract In order to examine small invertebrate scavenging fauna of tropical coral reef waters, baited traps were deployed in a coral reef of Bidong Island, Malaysia. The samples taken by the traps constituted only a single species of isopods (Cirolana sp.) and ostracods from three families (Cypridinidae, Cylindroleberididae, and

Paradoxostomatidae). Cirolanid isopods were never collected in net-samples suggesting they are hyperbenthic scavenging species. Judging from its sheer numbers in the bait-attracted community (86.1-98.6%), cirolanid isopods are one of the most important small invertebrate scavengers in coral reef waters of Bidong Island.

Abstrak Di dalam mengetahui kehadiran fauna invertebrat pemangsa di kawasan terumbu karang di perairan tropika beberapa perangkap berumpan telah diletakkan di sekitar kawasan terumbu karang di Pulau Bidong.

Perangkap berumpan tersebut telah berjaya memerangkap hanya satu spesies tunggal isopod (Cirolana sp) dan juga tiga famili ostrakod (Cypridinidae, Cylindroleberididae, dan Paradoxostomatidae). Didapati, isopod cirolanid tidak pernah direkodkan kehadirannya di dalam mana-mana persampelan yang menggunakan net, menunjukkan bahawa

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kumpulan organisma ini adalah sebagai spesies pemangsa hiperbentik. Merujuk kepada kehadirannya yg amat tinggi di dalam komuniti perangkap-berumpan tersebut (86.1-98.6%), didapati isopod cirolanid ini merupakan salah satu kumpulan invertebrate pemangsa kecil yang penting di kawasan terumbu karang di Pulau Bidong.

(Keywords: Bait-trap, Cirolana isopods, Coral reef, Ostracods, Scavenger)

INTRODUCTION small scavenging fauna have been conducted in temperate and boreal regions [e.g., 6, 7, 8, 9, 10, Predation has been thought to be a primary cause 11, 12, 13] and very few researches have been of fish mortality in coral reef ecosystems [1, 2]. done in tropical and subtropical regions [5], with However, substantial mortality is still observed in little information for species composition of small the absence of fish predators [3], probably due to invertebrate scavengers in tropical coral reef disease and atrophy. Such death would produce waters. This paper presents the preliminary results carrion or carcass, which is almost never observed on the composition of scavenging fauna collected on coral reefs (Britton and Morton, 1994). by baited traps in a tropical coral reef water of Recently it has been demonstrated that removal of Bidong Island, Malaysia in order to examine the carrion through large vertebrate scavengers potentially important scavengers for material (i.e., scavenging fish) is very rapid, and cycling in the reef ecosystems. consequently it leaves little evidence of carrion on reefs [4]. However, although large vertebrates are MATERIALS AND METHODS often the most noticeable carrion feeders at a carcass, small invertebrates such as amphipods The scavengers were collected in a coral reef at and isopods find and consume carcasses that Bidong Island (5°36,785’N; 103°3,527’E), off the vertebrates do not detect [5]. These small northeast coast of Peninsular Malaysia on 7-8 invertebrates also may make a significant June 2010 with baited traps similar to the method contribution to coral reef ecosystems as described in [13]. Ten 500 ml cylindrical plastic scavengers for recycling carcasses within reef bottles (diameter, 7 cm; height, 9 cm) were used systems. as traps. The top of each bottle was sealed with a plastic screw cap through which either large To date, most investigations on composition of (diameter, 2 mm) or small (1 mm) pores have

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been drilled. Five bottles were prepared for each The traps were retrieved the next day (1200 h). pore size and the number of pores was 6 in the 2 Before retrieving the traps, each bottle was placed mm pore traps and 25 in the 1 mm pore traps, in a plastic bag to prevent possible loss of resulting in total pore areas of 18.8 mm2 and 19.6 collected animals during transportation. mm2, respectively. Fresh bigeye scads (Selar Immediately upon arrival at the field laboratory, crumenophthalmus) were used as bait. Whole all samples were fixed in 5% buffered formalin bigeye scads were cut into round slices of ca. 1 cm seawater. Specimens from all traps were sorted, thickness, which were wrapped in a bag of nylon enumerated and identified to the lowest taxonomic gauze (mesh size, 100 μm). A bag containing ca. level whenever possible. For the net-zooplankton 30 g (wet wt) of bait was placed in 3 of the 5 traps samples, large or rare species were first sorted out, for both large and small pore traps. The six bottles then the remaining was split (1/10) of which all with bait were bound together and a diving weight zooplankton were identified and counted. For (2 kg) was attached on the bottom side of the isopods from the trap samples, the body length of bottles. randomly sampled 10 specimens from each trap were measured under a stereomicroscope (Wild, Similarly, the 4 bottles without bait were bound M10) using an eyepiece micrometer. together with a diving weight of 2 kg. Before setting the traps, all bottles were filled with RESULTS AND DISCUSSION filtered (Whatman GF/F) seawater. The traps with and without bait were placed on the sea-bottom by No animals were observed in the traps without SCUBA, keeping a distance of 2 m away between bait, while the baited traps constituted high each other. The placed depth was ca. 2.5-3 m. The density of isopods and ostracods. Isopods were traps were deployed ca. 1 hour before sunset overwhelmingly dominant (222-580 inds. trap-1) (1800 h). During the night (2000 h), constituting 86.1-98.6% of the total abundance, net-zooplankton was collected by horizontal followed by ostracods, which were much less towing (5 min) of a plankton net (mouth diameter, abundant (6-69 inds. trap-1) (Table 1). The isopods 50 cm; mesh size, 180 μm) in the layer ca. 1 m consisted of a single species (species not above the bottom close the traps for compare determined) belonging to Cirolana “parva” net-collected zooplankton with the bait samples. complex (Fig. 1). The body length of the Cirolana isopods ranged from 1.9 to 5.5 mm for all traps

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(average ± SD = 4.2 ± 1.0 mm). There was no (Gnorimosphaeroma sp.) was different from that significant difference in body length with different collected in the traps. The net samples contained pore size (Mann-Whitney U-test, P = 0.44). The 61 individuals of ostracods, of which only 2 ostracods from the traps consisted of three species individuals were also observed in the traps from the families Cypridinidae (Vargula sp.), (Vargula sp. and Xenoleberis sp., respectively). Cylindroleberididae (Xenoleberis sp.), and The net collected ostracods were dominated by Paradoxostomatidae (Cytherois sp.). The Euconchoecia sp., which accounted for 91.8% of ostracods Xenoleberis sp. and Cytherois sp. were the total net ostracods. It is evident that the collected only in the traps with 1 mm pore size. Cirolana isopods and three ostracod species There was no considerable difference in the total (Vargula sp., Cytherois sp. and Xenoleberis sp.) number of isopods and ostracods collected were attracted to the bait, considering their high between traps of different pore sizes abundance in the traps and their total absence (Mann-Whitney U-test, P = 0.827 for isopods and from the traps without bait. Attraction of large P = 0.275 for ostracods). number of isopods and ostracods, because of their sensitive chemoreceptive adaptation, to baited Most of the isopods were actively traps has been reported [14, 15]. moving/swimming in the traps with 2 mm pores at the time of recovery but most of them were dead The specialized mouthpart setae, presumed to be in the 1 mm pore traps probably due to the lack of chemosensory, in the cirolanid isopods as well as oxygen. Traps with 2 mm pores could have ostracods are assumed to function in detecting provided a set of live animals for experimental chemicals from the baits. Cirolana isopods (and studies, although they were fixed immediately in probably Cytherois ostracods) would be the present study.The sample from the plankton hyperbenthic scavengers considering their net towed near the bottom contained 15 taxonomic non-occurrence in the plankton net towed just groups (Table 1). The absence or negligible above the sea-bottom. Although we towed the occurrence from the traps of most of taxonomic plankton net only once in the present study, groups that were collected in the plankton net previous studies of net-zooplankton conducted in suggests that the present bait was less or not the same sampling location acknowledged no attractive to them. The net samples included 2 occurrence of cirolanid isopods in the net-samples individuals of isopods but the species throughout the year (Nakatomi unpubli.).

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Table 1. Individual numbers of organisms collected by traps with bait (#1-6) and without bait (#7-10) and by one-benthopelagic tow of plankton net over a coral reef at Bidong Island, Malaysia. Pore sizes (mm) indicate pore diamters that have been drilled on the traps. Taxon Trap sample Net sample With bait Without bait 2 mm pore 1 mm pore 2 mm pore 1 mm pore Trap #1 Trap #2 Trap #3 Trap #4 Trap #5 Trap #6 Trap #7 Trap #8 Trap #9 Trap #10 Fish larvae 0 0 0 0 0 0 0 0 0 0 70 Fish eggs 0 0 0 0 0 0 0 0 0 0 64 Gastropods 0 0 0 0 0 0 0 0 0 0 651 Bivalve larvae 0 0 0 0 0 0 0 0 0 0 150 Polychaete larvae 0 0 0 0 0 0 0 0 0 0 71 Chaetogonaths 0 0 0 0 0 0 0 0 0 0 71 Echinoderm larvae 0 0 0 0 0 0 0 0 0 0 220 Appendicularians 0 0 0 0 0 0 0 0 0 0 80 Mysids 0 0 0 0 0 0 0 0 0 0 97 Decapods (crab zoea) 0 0 0 0 0 0 0 0 0 0 234 Decapods (shrimp) 0 0 0 0 0 0 0 0 0 0 121 Tanais 0 0 0 0 0 0 0 0 0 0 10 Copepods 0 0 0 0 0 0 0 0 0 0 3,705 Isopods Sphaeromatidae Gnorimosphaeroma sp. 0 0 0 0 0 0 0 0 0 0 2 Cirolanidae Cirolana sp. 580 408 415 427 222 449 0 0 0 0 0 Ostracods Cypridinidae Vargula sp. 24 18 6 66 13 62 0 0 0 0 1 Philomedes sp. 0 0 0 0 0 0 0 0 0 0 3 Cylindroleberididae Xenoleberis sp. 0 0 0 1 0 2 0 0 0 0 1 Paradoxostomatidae Cytherois sp. 0 0 0 2 0 2 0 0 0 0 0 Halocyprididae Euconchoecia sp. 0 0 0 0 0 0 0 0 0 0 56

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